Ah just an idea how to make shops...
Ther are shop flags right same as house ones except theses ones make shops with 2 rooms... storage and the room with the tables. Now you drop items in the room with the tables and it occupies a spot on one of the tables. Then a window appears much like the player to player strading system. You select the amount you want too sell one for then the amount you are putting on the bench. Then when someone wants to buy it, they grab it and it comes up with another window(like the player trade system) and shows the price and asks how much the person would like to buy from the current stock in the storage room.